1. Field of the Invention
The present invention relates to the field of electroplating, and in particular to electroplating equipment.
2. Description of Related Art
The manufacture of semiconductor devices often requires the formation of electrical conductors (interconnects) on semiconductor wafers. Such interconnects may be formed by electroplating (depositing) an electrically conductive material, such as copper, onto the wafer.
The adoption of increasingly thin copper seed layers in the current wafer processing technologies leads to increasing challenges in obtaining uniform film profiles with copper (Cu) electroplating, due to increasing electrical resistance of the underlying seed layer. As the seed layer becomes thinner due to technology demands, increasing wafer resistance leads to stronger “terminal effects” (center-thin, edge-thick profile) and the film less uniform, which leads to unacceptable film profiles for subsequent processing. Hardware changes to reduce terminal effects for thin films (thicknesses of approximately 0.5 microns) often leads to worse uniformity for thick films (thicknesses approximately greater than 1 micron). More specifically, these thick films have problems with “edge roll-offs” (center-thick, edge-thin). Systematic empirical hardware optimizations to generate acceptable film profiles are prohibitively expensive in cost and time. Moreover, different types of wafers also lead to different film profiles.
Referring to FIG. 1, a cross-sectional view of a cylindrically-shaped electroplating cell of the prior art is shown, with the cross-sectional view being taken from the center axis to the outer periphery of the cell. The cell includes a plating cup with two concentric, annular or ring-like anodes 1a and 1b and an anode separator 2 which separates the two anodes. An anode chamber wall 3 defines an anode chamber for containing a plating solution. The anode chamber wall 3 includes an anode membrane outer support ring 4a and a porous anode membrane 4b attached thereto, with the anode membrane 4b traversing the anode chamber. A porous diffuser membrane 5a is affixed to the diffuser support ring 5b and traverses the anode chamber. A wafer holder 6, holding a wafer 7a, is mounted above the anode chamber wall 3. The surface of the plating solution in the anode chamber is in contact with a lower surface 7b of the wafer 7a, which forms a cathode. The lower surface 7b touches or is wetted by the plating solution during the plating process. The plating solution is provided to the anode chamber by way of a solution inlet nozzle 8 positioned on the center axis of the electroplating cell.